Power tapping apparatus

ABSTRACT

This apparatus can apply electrical power to a supply terminal from a pair of lines having a variable current and voltage. The apparatus has a voltage tapper and a series device. The voltage tapper is coupled to the lines and to the terminal for applying to the latter power drawn from the lines when their voltage difference exceeds a predetermined value. The series device is serially coupled into a given one of the lines for producing a voltage drop. The series device is coupled to the supply terminal for supplying power thereto as a predetermined function of the voltage drop of the series device.

BACKGROUND OF THE INVENTION

The present invention relates to power limiting apparatus and, inparticular, to equipment for establishing a duty cycle scaled tocorrespond with the measurement cycle of a peak demand meter.

It is known to reduce the duty cycle of power supplied to an airconditioning system to reduce the peak demand required from utilitylines. However, these systems have not considered the advantage ofscaling the repetition rate of the switching to complement a peak demandmeter. Such a peak demand meter measures over successive intervals of apredetermined duration the highest amount of energy consumed during theintervals. The highest energy demanded during these intervals is used bythe utility to set the billing rate to the consumer. Unfortunately, aconsumer who uses very little energy overall but occasionally requires ahigh peak power input may be billed at a substantially higher rate thanheavier users.

Known demand limiting systems generally require a continual potentialacross the affected lines for proper operation. Therefore, these knownsystems cannot be connected into a pair of lines that run to thethermostatic switch of an air conditioning system. When the thermostaticswitch is closed, there is no potential across the associated lines and,therefore, no potential is present for driving this demand limitingsystem.

Another consideration is switching of load more rapidly than they cantolerate. For example, once an air conditioning compressor is turnedoff, it must remain off for a minimum time interval to allow release offluids trapped therein. Premature operation can cause extreme stress anddamage.

Accordingly, there is a need for a simple and effective system whichlimits the peak power demands measured by a given demand meter and whichcan be connected to various points in the load circuit.

SUMMARY OF THE INVENTION

In accordance with the illustrative embodiments demonstrating featuresand advantages of the present invention, there is provided apparatus forapplying electrical power to a supply terminal from a pair of lineshaving a variable current and voltage. This apparatus has a voltagetapping means and a series means. The voltage tapping means is coupledto the lines and to the terminal for applying to the latter power drawnfrom the lines when their voltage difference exceeds a predeterminedvalue. The series means is serially coupled into a given one of thelines for producing a voltage drop. The series means is coupled to thesupply terminal for supplying power thereto as a predetermined functionof the voltage drop of the series means.

According to one embodiment of the present invention, the power demandthrough a pair of lines as measured by a peak demand meter is reduced.This peak demand meter can record the highest amount of average powerconsumed during successive time intervals, each interval having apredetermined duration. Preferably, a clock provides a periodic timingsignal to control a cycling switch. The cycling switch is seriallyconnected with power lines to periodically interrupt current from thepower lines with a period proportional to the period of the periodictiming signal. The period of the switch means is about as long as thepredetermined duration of the peak demand meter.

By employing apparatus and methods of the foregoing type, the peakdemand logged against a consumer can be reduced drastically. In oneembodiment where a peak demand meter measures average power consumedover a fifteen minute interval, a switch interrupts the power to a loadevery fifteen minutes to produce a 50% duty cycle. The peak power demandin this embodiment was therefore reduced by 50%, if the load would havebeen powered throughout the fifteen minute intervals.

In the situation where the load is an air conditioning unit, it has beenfound that periodic interruption does not necessarily reduce the comfortprovided by the air conditioner. This is because usually an airconditioning unit remains on for a relatively long interval followed bya relatively long off interval. Essentially, the preferred embodiment ofthe invention redistributes the relatively long off and on intervalsinto a series of short on (e.g. 71/2 minute) intervals followed by ashort off interval. Of course, the specific duration can be lengthenedor shortened depending upon the application. Consequently, the overallcooling effect remains the same except that now the air conditioningunit works on a more rapidly repeating duty cycle. As a result of theforegoing, the consumer pays for power demanded at a greatly reducedrate.

In a preferred embodiment the clock timing the cycling of power to anair conditioning or other unit, is sensitive to start-up considerations.For example, power restoration must be carefully regulated if power isinterrupted by external causes such as a power failure, operatorintervention, etc. The clock of the preferred embodiment sensesrestoration of power and resets to a phase in which power is kept offfor one half of the clock timing cycle. This feature avoids restorationof power after an unacceptably short interruption. This feature isespecially significant for air conditioning compressors which need timeto purge their cylinders before restarting. Premature restarting canoverstress these compressors. The preferred embodiment employs adetector coupled to the power lines to sense an increase in the peakmagnitude of line voltage. In one form the detector uses a diodecharging a capacitor to the present line voltage peak. A magnitudeincrease applied to this type of circuit can transfer resetting pulsesto the clock.

A significant advantage of the present invention is that it can operateon virtually any of the lines controlling or powering the load. Considera pair of lines to a thermostatic switch which when the switch is closedhas zero potential across them. In a preferred embodiment, an energystorage system is charged when the thermostatic switch is open so thatan energizing potential can be produced even when the thermostaticswitch subsequently closes. It is also preferable to include a serieselement such as a zener diode in one of the lines so that a usablevoltage exists even if the thermostatic switch is closed. Although thereis practically no voltage drop across the closed switch, the currentflowing therethrough can be used to drive the zener to a stable voltagethat can be used to charge the energy storage system. Thus the energystorage system (which can be a capacitor or a battery) is chargedcontinuously whether the thermostatic switch is open or closed, so longas the utility lines are still in a condition to deliver power.

In one embodiment, a pulse generator drives a divider to cycle a triacon and off every fifteen minutes. This triac is in the thermostaticcircuit of an air conditioning system. In other embodiments, however,the triac can either control the current directly delivered to a load orcurrent delivered to a relay controlling the load current.Alternatively, the triac controls a larger triac which in turn drives acoil operating a high current contactor.

BRIEF DESCRIPTION OF THE DRAWINGS

The above brief description as well as other objects, features andadvantages of the present invention will be more fully appreciated byreference to the following detailed description of the presentlypreferred but nonetheless illustrative embodiments in accordance withthe present invention when taken in conjunction with the accompanyingdrawings wherein:

FIG. 1 is a schematic diagram of apparatus according to the principlesof the present invention; and

FIG. 2 is a schematic diagram of an embodiment which is an alternate tothat of FIG. 1.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Referring to FIG. 1, the illustrated apparatus can limit power deliveredfrom power lines 10 through peak demand meter 12. Peak demand meter 12,in this embodiment, measures the amount of average power drawn fromutility lines 10 during successive time intervals of a predeterminedduration. Peak demand meter 12 records the highest amount of powerconsumed during those successive time intervals (e.g. each 1/4 hour).The largest measurement thus made is defined by the utility as the peakdemand of the consumer from utility lines 10. This peak demand togetherwith the billing rate establishes the cost for demand wattage.Therefore, the higher the peak demand, thus recorded, the higher thecost. Pair of lines 14 from meter 12 connect to the primary oftransformer T1 and the series combination of load 16 and relay contacts18 as well. Load 16, in this embodiment, is an air conditioning unit,however, it will be appreciated that the load may be any deviceconsuming electrical energy. The secondary of transformer T1 is seriallyconnected with another load, in this embodiment, relay coil 20 whichoperates contacts 18. The serial combination of the secondary oftransformer T1 and relay coil 20 connects across a pair of linesidentified herein as lines 22A and 22B. A zener diode Z1, acting as aseries means has its cathode connected to line 22A and its anode to themain electrode of a switching means, shown herein as bidirectionalcurrent conducting device Q1. Its other main electrode connects to oneterminal of thermostatic switch 24, whose other terminal connects toline 22B. Thus connected, device Q1 (a triac) can complete the circuitfrom the secondary of transformer T1 through zener Z1 and thermostaticswitch 24 to the relay coil 20. It will be appreciated, however, thatfor some embodiments relay coil 20 (or switch 24) may be eliminated andswitch 24 (or coil 20) is replaced with a load circuit. This loadcircuit could be any energy consuming device which is operable at areduced duty cycle. Alternatively, the position of relay coil 20 can betransposed with thermostatic switch 24 to produce a functionallyequivalent circuit. Also, the position of zener Z1 can be changed asfurther explained hereinafter. This change is suggested by zener diodesZ2 and Z3. Zener Z2 is serially connected between triac Q1 and switch 24(cathode to switch 24) while zener Z3 is serially connected betweenswitch 24 and line 22B (anode to switch 24). Of course zeners Z2 and Z3are shown shorted since these alternate positions are not used herein.

An energy storage means is shown herein as electrolytic capacitor C2,although a charge storage device such as a nickel-cadmium battery can beused instead. The negative terminal of capacitor C2, identified by aterminal bearing a negative symbol, connects to similarly identifiedterminals in this schematic as well as to the anode of zener diode Z1.The positive terminal of capacitor C2, identified as a supply terminalbearing a positive symbol, connects to similarly identified terminals inthis schematic.

A voltage tapping means is shown herein as a unidirectional conductingdevice CR1 serially connected to resistor R1. Resistor R1 is connectedbetween line 22B and the anode of diode CR1, its cathode being connectedto the positive terminal of capacitor C2. Another voltage tapping meanshas a resistor R9 connected between line 22A and the anode of diode CR2,whose cathode connects to the positive terminal. A voltage regulatingzener diode Z4 has its cathode connected to the positive terminal andits anode connected to the anode of zener diode Z1.

Resistor R2 is connected between the anode of zener diode Z1 and thegate electrode of triac Q1. Resistor R3 connects between this gateelectrode and the emitter of NPN transistor Q2, whose collector isconnected to the previously mentioned positive terminal and whose baseis connected to a clock means. This clock means includes a divider 28,having a plurality of output terminals A, B and C. Those outputterminals are part of a selection means whereby the base of transistorQ2 can be connected to any of the output terminals. In this embodiment,divider 28 can divide incoming pulses by a maximum factor of 2¹⁴(16,384). Terminal C, to which the base of transistor Q2 is presentlyconnected, provides this maximum division. Accordingly an 18.2 Hertzoscillator input applied to input terminal 34 provides an output cycleof 900 seconds.

A reset means is shown herein as a detector 35 having a unidirectionalconducting device CR6, whose anode connects to line 22B. A capacitiveelement C4 has one terminal connected to the resetting input R ofdivider R and the other terminal connected to a resistive element R12which leads to the negative terminal. Resistor R14 connects between thecathode of diode CR6 and the junction of resistor R12 and capacitor C4.Resistive element R16 connects between resetting input R and thenegative terminal.

A pulse generator is shown herein as a pair of logic gates, NAND gates30 and 32. The output of NAND gate 30 connects to both inputs of NANDgate 32, whose output connects to one terminal of capacitor C1. Itsother terminal connects to one terminal of resistor R13, whose otherterminal connects to both inputs of NAND gate 30. The series combinationof resistor R4 and variable resistor R5 connects between the output ofNAND gate 30 and the junction of resistor R13 and capacitor C1. Theoutput of NAND gate 32 is identified as an input test terminal 34. NANDgate 30 and 32 as well as divider 28, receive power from capacitor C2 asindicated by the positive and negative terminals leading to them.Terminal 34 is the input of divider 28.

Referring to FIG. 2, identically labeled elements are the samecomponents connected in the same manner as previously described. Again,output C of divider 28 connects to the base of transistor Q2 to drivethat transistor. Serially connected between the negative terminal andthe emitter of transistor Q2 is the series combination of resistors R7and R6. This negative terminal is a negative battery terminal fornickel-cadmium battery 40, whose positive terminal connects to one leadof the secondary of transformer T2, its other lead connecting to thecathode of diode CR3. Resistor R8 connects between the negative terminalof battery 40 and the anode of diode CR3. Connected in parallel with theprimary of transformer T2 are the output lines, lines 46A and 46B, ofpeak demand meter 42, whose input lines connect to utility lines 44.Line 46A connects to the negative terminal of battery 40 and to oneterminal of resistor R10, whose other terminal connects to one mainterminal of switching device Q4, its other main terminal connecting tothe cathode of diode CR4. Capacitor C3 is connected in parallel withresistor R10. The anode of diode CR4 connects to line 46B. The gate ofswitching device Q4 (in this embodiment, a triac) connects to thejunction of resistors R6 and R7. A semiconductor switch, shown herein astriac Q5, has its trigger electrode connected to the junction of triacQ4 and resistor R10. Line 46A connects to one switching electrode oftriac Q5, its other switching electrode connecting to one terminal ofrelay coil 48, whose other terminal connects to line 46B. Coil 48 ispart of relay 50 and drives relay contacts 52 which connect between line46A and one terminal of load 54, whose other terminal connects to line46B.

The previously illustrated reset means 35 is shown connected as beforeto resetting terminal R of divider 28 while the anode of diode CR6 isshown connected to line 46B. A selectable series means is shown hereinas shorted zener diode Z6 serially connected in line 46A between meter42 and contacts 52. This zener could provide a voltage when line 46A isconducting should the voltage drop across load 54 be insufficient or ifload 54 were replaced with a switch.

To facilitate an understanding of the principles associated with theforegoing apparatus, its operation will be briefly described. Referringfirst to FIG. 1, it will be presumed that thermostatic switch 24 opens(and closes) regularly. Initially assuming triac Q1 is non-conductive,the open secondary voltage of transformer T1 appears across lines 22Aand 22B. Accordingly, diodes CR1 and CR2 act as a full wave rectifierproducing pulses that charge capacitor C2. Were triac Q1 conducting withswitch 24 closed, a regulated unipolar, pulsating voltage drop wouldappear across zener diode Z1 and therefore effectively across lines 22Aand 22B. Therefore diode CR2 would act as a half-wave rectifier againcharging capacitor C2. Therefore capacitor C2 is charged regardless ofthe state of switches 24 and Q1 provided transformer T1 is powered.

Also for some embodiments, elements R9 and CR2 may be removed, zenerdiode Z1 shorted and zener diode Z2 or Z3 unshorted. This simplifiedcircuit causes half wave charging through diode CR1 whether lines 22Aand 22B are conducting or not. Consequently, the positive and negativeterminals have across them a predetermined potential. Due to theblocking action of diode CR1, this potential persists even though thepotential across lines 22A and 22B may briefly fall to zero.

Therefore, an energizing potential is applied to the clock comprisingdivider 28 and NAND gates 30 and 32. Since positive feedback is providedby resistor R13 and capacitor C1, NAND gates 30 and 32 oscillate. Thefrequency of this oscillation can be adjusted by variable resistor R5 ina conventional fashion. This adjustment is set to produce a pulse trainat terminal 34 having a repetition rate of 18.2 Hertz. This 18.2 Hertzsignal is divided by binary divider 28 by the factor 2¹⁴. Consequently,the output produced on terminal C has a period of approximately fifteenminutes, 7.5 minutes on and 7.5 minutes off. It will be appreciated, ofcourse, that this period can be altered and its duty cycle varieddepending upon the specific application. The selected output terminal ofdivider 28 can be changed to reduce that period of fifteen minutes byone half or one quarter, or any division of 2, as desired.

Selected output C of divider 28 renders transistor Q2 alternativelyconductive and nonconductive from its collector to its emitter.Consequently, the voltage between the gate electrode of triac Q1 andline 22A alternates from positive to zero potential, rendering triac Q1alternately conductive and nonconductive, respectively.

It is now assumed that thermostatic switch 24 closes. Therefore, triacQ1 is able to conduct through actuated switch 24 at a period and dutycycle determined by divider 28. Therefore, current flows through relaycoil 20 at a 50% duty cycle, cycling every fifteen minutes. As a result,air conditioning load 16 operates for 71/2 minutes and is then disabledfor 71/2 minutes. It is recommended that for air conditioning loads theoff period be reasonably long so the compressors can dischargerefrigerant that may be temporarily trapped in the compression chamberof the compressor. An attempt to operate the compressor before therefrigerant has discharged will cause an excessive load on thecompressor piston which can fatique or break it.

As a result of the foregoing, current is supplied to air conditioningload 16 from peak demand meter 12 for only one half of its timemeasurement interval of fifteen minutes. Therefore, the peak loadmeasured by meter 12 is half of what would have been measured in theabsence of the apparatus of FIG. 1.

When switches Q1 and 24 are closed, the essentially zero voltage acrossthem is also applied across diode CR6 and resistors R14 and R12.Accordingly, the terminal of capacitor C4 connected to resistor R12 isat the same potential as the negative terminal. Capacitor C4 is sized sothat within a minute or so it discharges through resistors R12 and R16to zero volts. When switch 24 (or triac Q1 for that matter) opens, apulsating positive voltage is coupled through diode CR6 and capacitor C4to resetting input R until capacitor C4 charges to the positive peak ofline 22B. Consequently divider 28 is reset to an off cycle, therebyopening triac Q1 for 7.5 minutes. This ensures that power removed fromcoil 20 cannot be restored immediately. This prevents unacceptably rapidpower restoration that may damage air conditioning compressors.Alternatively, the utility lines may fail and cause a power interruptioneventually resulting in a discharge of capacitor C4. Consequently,restoration of power again causes coupling of a pulsating positivevoltage through diode CR6 and capacitor C4 to resetting input R untilcapacitor C4 charges to the positive peak of line 22B. Again divider 28is reset to an off state for 7.5 minutes to prevent prematurerestoration of power.

It will be appreciated that resetting of divider 28 can be through itsreset or set input and accordingly signals may require inversion toaccount for such a reconnection.

The operation of the apparatus of FIG. 2 is similar, divider 28producing pulses which alternately render transistor Q2 conductive andnonconductive. In this embodiment, transformer T2 is provided primarilyto maintain the charge on battery 40 through resistor R8 and diode CR3.

Since transistor Q2 is alternately conductive and nonconductive, italternates the gate of triac Q4 between a positive or zero potentialwith respect to its main electrode connected to resistor R10.Consequently, triac Q4 conducts at a 50% duty cycle over a period offifteen minutes. This produces a pulsating positive voltage acrossresistor R10 which renders triac Q5 conductive at a 50% duty cyclehaving a period of fifteen minutes. As a result, a circuit isperiodically made through triac Q5 from the output terminals of meter 42through relay coil 48. Consequently, relay contacts 52 cycle everyfifteen minutes at a 50% duty cycle. Therefore, load 54 is alsoenergized at a 50% duty cycle with a fifteen minute period. Therefore,as before, peak demand meter 42 reads a peak demand which is only halfof what would be read in the absence of the apparatus of FIG. 2.

Again, reset means 35 place divider 28 at the beginning of an off cycleif power is interrupted due to a failure of utility lines 44.Furthermore, the opening of switch 52 also produces a sudden increase inthe peak magnitude of voltage across lines 46A and 46B which againresets divider 28 to the beginning of an off cycle, ensuring that poweris not rapidly reapplied to load 54. The latter increase in voltageacross lines 46 is due to the usual increase in line voltage under noload conditions. Of course, if this no load fluctuation is unusablysmall, a small inductor can be inserted in either line 46A or 46Bimmediately after meter 42.

Finally in the event load 54 is replaced with a switch, zener diode Z6can be unshorted to provide power to charge battery 40, in a mannersimilar to zener Z1 of FIG. 1.

It is to be appreciated that various modifications may be implementedwith respect to the above described preferred embodiments. For example,in systems requiring or allowing the switching of direct currentvoltages, thyristors or other types of switching devices may besubstituted for the illustrated triacs. Furthermore, various types ofloads can be switched and for loads that need not remain off for aminimum period of time, the repetition rate may be substantiallyincreased. In addition, some embodiments may use a duty cycle differingfrom 50%. For thermostatically controlled embodiments, the apparatus canbe inserted into the lines leading to either: the thermostat, theutility lines or the relay coil operated by the thermostat. In otherembodiments, the apparatus may be inserted in a line running directlyfrom the utility lines to the load. While a nickel-cadmium battery isillustrated, other batteries may be employed in different embodiments.Also instead of integrated circuitry, discrete circuits may be used.Moreover, various components may be substituted for the illustratedcomponents depending upon the desired power, speed, stability, size,permissible heating, accuracy, etc. It is also anticipated that to avoidthe effect of humidity or corrosive effects, the circuit may be mountedon a printed circuit board and completely encapsulated in polyurethane.

It is also noted that for test purposes, a high frequency signal may beinjected into the input of the divider to cause it to cycle much morerapidly then designed, thereby reducing the test time.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is therefore to beunderstood that within the scope of the appended claims, the inventionmay be practiced otherwise than as than specifically described.

What is claimed is:
 1. Apparatus for applying electrical power to asupply terminal from a pair of lines having a variable current andvoltage, comprising:a voltage tapping means coupled to said lines and tosaid terminal for applying to the latter power drawn from said lineswhen their voltage difference exceeds a predetermined value; and aseries means serially coupled into a given one of said lines forproducing a voltage drop, said series means being coupled to said supplyterminal for supplying power thereto as a predetermined function of thevoltage drop of said series means.
 2. Apparatus according to claim 1wherein said voltage tapping means comprises:a unidirectional conductingdevice coupled between said supply terminal and one of said lines. 3.Apparatus according to claim 2 wherein said unidirectional conductingdevice is coupled to said given one of said lines.
 4. Apparatusaccording to claim 1 wherein said series means comprises a zener diodeand wherein said voltage tapping means includes a charge storage devicecoupled between one of said lines and said supply terminal.
 5. Apparatusaccording to claim 1 wherein said lines have connected between adjacentends thereof a switch, closing of said switch reducing the voltagedifference between said lines below said predetermined value, wherebysaid series means and not said voltage tapping means is operable tosupply power to said supply terminal.
 6. Apparatus according to claim 1further comprising:clock means for providing a timing signal; and switchmeans serially connected in one of said lines for interrupting it. 7.Apparatus according to claim 6 wherein said clock means is powered bypower from said supply terminal.
 8. Apparatus according to claim 7wherein said lines are coupled to utility lines through a peak demandmeter, said meter being operable to record the highest amount of averagepower consumed during successive time intervals, each having apredetermined duration, said clock means having a period about as longas said predetermined duration, said switch means being actuated onceduring said period.
 9. Apparatus according to claim 8 wherein the dutycycle of said switch means is about 50% and wherein said voltage tappingmeans includes a charge storage device coupled between one of said linesand said supply terminal.
 10. Apparatus according to claim 9 whereinsaid lines carry alternating current and wherein said switch meanscomprises a bidirectional current conducting device having a gateelectrode and a pair of main electrodes, said gate electrode beingcoupled to said clock means.
 11. Apparatus according to claim 10 whereinsaid clock means comprises:a pulse generator; and a divider driven bysaid generator for producing a square wave signal at a frequencyproportional to and lower than the repetition rate of said pulsegenerator.
 12. Apparatus according to claim 11 wherein said divider hasa plurality of output terminals each producing a signal having adifferent frequency, said switch means having:selection means forconnecting said switch means to any one of said plurality of outputterminals whereby the period of said switch means is renderedadjustable.
 13. Apparatus according to claim 12 wherein said pulsegenerator comprises:a pair of logic gates connected to produce positivefeedback.
 14. Apparatus according to claim 1 comprising:a clock meansfor providing a periodic timing signal, said clock means beingresettable to change the phasing of said timing signal; a switch meansserially coupled to at least one of said lines to periodically interruptcurrent of said lines with a period proportional to the period of saidperiodic timing signal; and reset means coupled to at least one of saidpower lines for resetting said clock means in response to the averagemagnitude of voltage across said lines increasing by a predeterminedextent.
 15. Apparatus according to claim 14 wherein resetting of saidclock means phases the timing signal to cause said switch means tointerrupt current of said lines.
 16. Apparatus according to claim 15wherein said timing signal is divisible into an on interval and an offinterval, resetting of said clock means bringing said timing signal tothe beginning of said off interval.
 17. Apparatus according to claim 16wherein said reset means comprises:peak detector for sensing the peakvoltage excursions on said line and for producing a reset signal inresponse to an increase in said excursions.
 18. Apparatus according toclaim 16 wherein said reset means includes:a capacitive element; and aunidirectional conducting device serially connected with said capacitiveelement between said clock means and a first one of said lines. 19.Apparatus according to claim 18 further comprising:a resistive elementconnected between one terminal of said capacitive element and a secondone of said lines.